Since the late 1930s the so-called acoustic sounding, or echometering, method has been used in the oil industry for taking distance measurements in an oil well or borehole, see U.S. Pat. No. 2,927,301, Booth, Measurement of liquid levels in wells. The acoustic sounding method involves sending a short, sharp, clear, loud bang sound down an oil well or borehole and using a transducer to “listen” to the echoes reflected back. The signal from the transducer is usually recorded for analysis which is usually performed by a separate device: see U.S. Pat. No. 2,209,944, Walker, Method of measuring location of obstructions in deep wells, and U.S. Pat. No. 2,232,476, Ritzmann, Method and apparatus for measuring depth in wells.
As explained in these patents and other literature, the acoustic sounding method not only determines the distances between the source of the sound and the causes of the echoes, but also determines the physical nature of the causes of the echoes based on the frequency, amplitude, and other attributes of the sound being reflected back. For example, in its application in oil wells the acoustic sounding method can not only determine the distance to the “bottom” of the well, i.e. the fluid level of the well, but it can also determine other attributes and anomalies, such as wax, scale, or gas build-up and other obstructions, encountered down the well based on the nature of the echoes received at the wellhead by the transducer.
Further the acoustic sounding method itself has other distance measuring and obstruction analysis applications beyond its use in oil wells. As an example, an early application of the acoustic sounding method was used by the postal service in New York City in the early 1900s to locate mail bags stuck in mail transportation tubes.
One common method for generating the sound needed for the acoustic sounding method is to use an air or gas pressurized chamber which is discharged at or near the wellhead or the void to be analyzed. As described in U.S. Pat. Nos. 4,750,583 and 4,646,871, Wolf, Gas-Gun for Acoustic Well Sounding (hereinafter “Wolf”) the sound generated by the pressurized chamber comes from the energy released by the equilibration of the different pressures between the chamber and the wellhead or the void. A different, earlier method for generating the sound needed for the acoustic sounding method was to fire a blank cartridge from a firearm at the wellhead. Accordingly the oil industry has coined the term “sound gun”, “echo gun”, “acoustic gun”, or simply “gun” to generally describe devices that produce the sound needed for the acoustic sounding method.
Although acoustic generators, acoustic guns using a pressurized gas chamber, have been used for many years, these acoustic generators have failed to address a number of issues in their use and have failed to yield the full benefits of the acoustic sounding method as an analytical tool for measuring distances and analyzing physical attributes.